The present invention relates to metal oxide particles and their preparation. More specifically, it relates to the production of zinc oxide.
Zinc oxide is a well-known compound and has several well-known utilities. It is especially useful in the production of electronic components such as varistors. See, e.g., U.S. Pat. Nos. 4,460,623; 4,320,379; 4,243,622; 4,285,839; and 4,374,049. The availbility of spheroidal zinc oxide of submicron, uniform particle size is important in the preparation of varistors. The non-linearity of the varistor device arises from a thin, insulating secondary phase grain boundary. The smaller the grain size of the zinc oxide, the more grain boundaries per unit volume. Thus, smaller grains allow the production of varistors having higher voltage ratings per unit volume. The more uniform the microstructure, the sharper the break from linear to non-linear behavior. See, e.g., Ceramic Bulletin, Vol. 63, p. 278 at p. 280; Lauf, R. J. and Bond W. D. (1984). However, current technology is incapable of producing zinc oxide of submicron, uniform particle size.
A conventional method of producing zinc oxide involves burning zinc metal vapors. See, e.g., Zinc Chemicals, by M. Farnsworth and C. H. Kline, pp. 47-50; Zinc Institute, Inc., NY, NY (1983). However, this method has relatively poor control over product particle size. Similary, other proposed methods have not been proven successful in the preparation of spheroidal zinc oxide of submicron particle size and relatively uniform particle size distribution. In view of the lack of success of prior art methods and the deficiencies inherent therein, and in view of the need for spheroidal zinc oxide of submicron particle size and uniform size distribution, it would be desirable to have a process which could prepare the desired zinc particles.